A plaintiff (Π in legal shorthand), also known as a claimant or complainant, is the party who initiates a lawsuit (also known as an action) before a court. By doing so, the plaintiff seeks a legal remedy, and if successful, the court will issue judgment in favor of the plaintiff and make the appropriate court order (e.g., an order for damages).

In some jurisdictions the commencement of a lawsuit is done by filing a summons, claim form and/or a complaint — these documents are known as pleadings — that set forth the alleged wrongs committed by the defendant or defendants with a demand for relief. In other jurisdictions the action is commenced by service of legal process by delivery of these documents on the defendant by a process server; they are only filed with the court subsequently with an affidavit from the process server that they had been given to the defendant(s) according to the rules of civil procedure.

Not all lawsuits are plenary actions, involving a full trial on the merits of the case. There are also simplified procedures, often called proceedings, in which the parties are termed petitioner instead of plaintiff, and respondent instead of defendant. There are also cases that do not technically involve two sides, such as petitions for specific statutory relief that require judicial approval; in those cases there are no respondents, just a petitioner.

A plaintiff identified by name in a class action is called a named plaintiff.

The party to whom the complaint is against is the defendant; or in the case of a petition, a respondent. Case names are usually given with the plaintiff first, as in Plaintiff v. Defendant.

"Complainant" may also denote the complaining witness in a criminal proceeding.

United Kingdom

In England and Wales, the term Claimant has replaced Plaintiff after the Civil Procedure Rules 1998 came into force in 26 April 1999. In Scottish law, a plaintiff is referred to as a pursuer and a defendant as a defender.

Elsewhere

In Hong Kong and the United States, a plaintiff is still referred to as a plaintiff. Americans traditionally limit the application of terms such as "claimant" and "claim form" to extrajudicial process in insurance and administrative law. After exhausting remedies available through an insurer or government agency, an American claimant in need of further relief would turn to the courts, file a complaint (thus establishing a real court case under judicial supervision), and become a plaintiff.

Etymology

The word plaintiff can be traced to the 1278 and stems from the Anglo-French word pleintif meaning 'complaining' from pleint. It was identical with plaintive at first and it is this form that receded into legal usage with the -iff spelling in the 1400s.